docs: def parse_block_scalar_indent(token_class):
          """Process indentation spaces in a block scalar."""
          def callback(lexer, match, context):
              text = match.group()
              if context.block_scalar_indent is None:
                  if len(text) <= max(context.indent, 0):
                      context.stack.pop()
                      context.stack.pop()
                      return
                  context.block_scalar_indent = len(text)
              else:
                  if len(text) < context.block_scalar_indent:
                      context.stack.pop()
                      context.stack.pop()
                      return
              if text:
                  yield match.start(), token_class, text
                  context.pos = match.end()
          return callback